Drive circuit for counting tubes



1960 J. E. ADAMS 2,949,564

DRIVE CIRCUIT FOR COUNTING TUBES Filed April 8, 1958 OUTPUT IN VEN TOR. JOHN E. ADAMS BY N/ ATTORNEY DRIVE CIRCUIT FOR COUNTING TUBES John E. Adams, Burlington, Mass, assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, DeL, a corporation of Delaware Filed Apr. 8, 1958, Ser. No. 727,113

Claims. (Cl. 315-84.6)

This invention relates to electronic counting devices and more particularly to drive circuits for gas-filled glow transfer counting tubes.

Electronic counting of electrical impulses is a relatively old concept, counting having heretofore been accomplished by a variety of circuits usually having a plurality of bistable stages, and more recently incorporating counting tubes having several counting stages within one tube envelope. The latter tubes are generally, although not necessarily, constructed to provide for a count of ten and may be cascaded to provide a decimal counting system to any desired order of magnitude.

One category of these counting tubes is the so-called gas-filled glow transfer counting tube of which a number of types have been developed. All of the types, however, are multiple element tubes wherein a glow on one of the elements indicates visually and electrically a unit of data. Impulses reaching the tube are counted and indicated by the change of the position of the glow from one element to another element in a predetermined pattern.

The present invention is concerned with a glow transfer tube of the type having a central anode and three sets or groups of cathodic electrodes. One set of the cathodic electrodes serves as the main or count indicating cathodes, and the other two sets are the so-called guide electrodes or guides. The transfer action of these tubes requires a driving circuit to convert input pulses into signals which are capable of switching the position of the glow from a main cathode to intervening guide electrodes and then on to the next main cathode in proper sequence.

The envelope of tubes of this type is gas filled and has a disk shaped anode located at its center. Arranged in an annular an-ay about the anode are thirty (for a decimal counting system) equally spaced rod-like cathodic electrodes. Every third cathodic electrode is designated as a main or count indicating cathode, which may be electrically connected together, but generally with one or more unconnected to the balance to provide independent electrical outputs. The remaining cathodic electrodes are divided into two groups, all of the electrodes of each group being connected together to form two sets of guide or transfer electrodes. Switching of the glow from one main cathode to the next main cathode to effect a count is accomplished in the following manner.

The potential of one set of guide electrodes is lowered to a point where the glow will leave its position on the main cathode and transfer to the nearest guide electrode of that set. The potential of the second set of guide electrodes is then lowered while the potential of the first set is allowed to return to its normal value. When the potential on the second set is sufiiciently lower than that on the first set, the glow will transfer from its position on a guide electrode of the first set to the adjacent guide electrode of the second set. The potential of the second Set of guide electrodes is then allowed to return to its normal value. The normal potentials on the second set of guide electrodes and on the main cathodes are such that the glow will then move from the second guide electrade to the adjacent main cathode. Thus, the glow is moved in a predetermined direction from one main cathode via two guide electrodes to the next main cathode to effect a count. 7

The result described above is achieved by means of a driving circuit for the tube, capable of providing in response to a single input pulse successive overlapping pulses of the proper character to ignite the guide electrodes. designed for accomplishing this function, for example, the circuits disclosed in applicants copending applications Serial No. 606,142, filed August 24, 1956, now Patent 2,845,578, issued July 29, 1958, Serial No. 619,- 536, filed October 31, 1956, now Patent 2,849,655, issued August 26, 1958, and Serial No. 633,590, filed January 11, 1957, now Patent 2,864,034, issued December 9, 1958. Each of these circuits have the general characteristic of overlapping ignition of the guides from single pulses, the simplest form being one in which an input pulse is applied directly to one set of guide electrodes and through an appropriate delay circuit to the second set of electrodes. Two characteristics of such drive circuits which contribute to reliability and range of response are aperiodicity and positiveness of action.

It is an object of the present invention to provide a reliable electron discharge impulse counting circuit capable of operating at high input pulse rates.

Another object of the invention is to provide a driving circuit for a gas-filled glow transfer counting tube having the characteristics of aperiodicity and positiveness of action with a minimum of circuit components.

In accordance with the present invention, aperiodicity is achieved by the use of a single reactive component, and the positive action is obtained through the utilization of the inherent characteristics of a pentode electron tube. The anode of the pentode is connected to the first set of guide electrodes, and the screen grid of the pentode is connected to the second set of guide electrodes, the control grid being biased to cut-off in the quiescent condition of the tube. A capacitor is connected between the screen grid and a point of reference potential and together with the characteristics of the pentode achieves overlapping ignition pulses on the first and second guide electrodes in response to a single positive going input pulse to the control grid of the pentode. Briefly, the leading edge of the input pulse causes a rising anode current in the pentode which creates a negative going voltage on the anode and on the first guide electrodes, thereby igniting or causing a glow to appear between the first guide electrode and the anode. The reduction in anode voltage causes an increase in the screen current of the pentode, which discharges the capacitor connected thereto and creates a negative going voltage on the screen grid and on the second guide electrodes. During the period or duration of the pulse, both guides are ignited equally or one more than the other, depending upon the exact characteristics of the pentode used. With the occurrence of the trailing edge of the input pulse, the pentode current is cut off, immediately extinguishing the first guide, and when the glow current has charged the capacitor to a voltage more positive than that of the next adjacent cathode, the glow is transferred from the second guide to that cathode.

A better understanding of the present invention, together with other objects, features and advantages, will be had from the following detailed description of a preferred embodiment read in connection with the accompanying drawing the single figure of which is a schematic A number of circuits have heretofore beendiagram of the drive circuit and a representative glow transfer counter tube.

In the drawing, the counting tube is shown at and includes a disk shaped anode 11 surrounded by slim rodlike cathodic elements arranged in an annular row. Each third cathodic electrode 12, 12a, 12b, 12c and 12d is designated as a main or count-indicating cathode. To avoid undue complication of the drawing and to simplify the explanation of the invention there is illustrated a counting tube having only five rather than the ten stages previously noted as being preferred for decimal counting, but the ten stage device would, of course, operate in the same manner as that to be described.

Adjacent each main cathode are two guide electrodes. For example, adjacent main cathode 12 in a clockwise direction is a guide electrode 13, guide electrode 13a adjacent main cathode 12a, and so on. Similarly, guide electrodes 14, 14a, 14b, 14c and 14d lie adjacent main cathodes 12, 1'2a, 12b, 12c andlZd respectively. Guide electrodes 13, 13a, 13b, 13c and 13d are all electrically connected together by the connection shown as the innermost ring in the drawing. Guide electrodes 14, 14a, 14b, 14c and 14d are similarly connected together through the middle wiring ring. Main cathodes 12, 12b, 12c and 12d are also connected together through the outermost wiring ring, cathode 1211 being independent of direct connection to the ring and serves as an output terminal for the tube.

The electrodes thus far described are contained in an envelope, designated by the dotted circle 10a, which is filled with a suitable gas. Although the interconnections between the several electrodes are illustrated as being externally of the envelope, it is the usual practice to make these connections internally of the tube.

The anode 11 of the counter tube is connected through a resistor 15 to a source of positive voltage, represented by terminal 16. The main cathode 12a is selected as the output cathode and is connected through a resistor 17 to another and lower positive potential, designated as terminal 18. An output terminal 19 is connected to the main cathode 12a, and the next adjacent main cathode 12b (as well as the other main cathodes) are connected to the source of potential at terminal 18. Similar connections may be provided for other main cathodes Where it is desired to obtain additional outputs, but in the disclosed embodiment the four remaining cathodes are all connected directly to terminal 118.

The driving circuit of the present invention comprises a pentode 20, for example a 6AU6, the anode of which is connected to one set of guide electrodes; namely, 13, 13a, 13b, 13c and 13d, and the screen grid is connected to the other set of guide electrodes; namely, 14, 14a, 14b, 14c and 14d. The screen grid is also connected to ground through capacitor 21 which is the only reactive component of the driving circuit. Positive going input pulses are applied to the driving circuit at terminal 22 through coupling condenser 23 and grid resistor 24. The suppressor grid and cathode of the pentode are connected together and to a source of positive potential, designated at terminal 25, of a magnitude to bias the tube oli in the absence of input pulses.

In a typical circuit of the type described and illustrated, the tubes employed were a Sylvania type 6802 as the glow transfer tube 10, and a type 6AU6 as the pentode 20. The potentials at terminals 16, 18, and 25 were respectively 640 volts, 160 volts and 10 volts positive. Resistor 15 may typically be 600,000 ohms, resistor 17, 68,000 ohms, and resistor 24, l megohm. With these parameters, a capacitor of 220 micromicrofarads was found satisfactory for the capacitor 21.

Considering the disclosed circuit energized as described, a glow will take place immediately between one of the main cathodes and the anode by reason of the difierential in potential between the anode and cathodes. The particular main cathode which assumes a glow-will be determined by some asymmetrical condition existing in the tube or circuit which causes a lower potential to appear at that main cathode. In the absence of pulses, all main cathodes are at a lower potential than the guide electrodes and consequently the glow always appears at a main cathode. In the circuit being considered, the main cathodes are at 160 volts, the guide electrodes being at a somewhat higher potential. Although pentode 20 is cut off by the bias from terminal 25, a certain minimum plate current is actually flowingin the pentode. This minimum current, determined by the requirement for electrons to neutralize the stray gaseous ions present in the annular zone between the anode and cathode array of the counter tube, at points other than the zone of the existing visible glow, is of such a value that the voltage drop across the pentode is considerable. This voltage, and consequently the voltage on the guide electrodes is considerably in excess of the 160 volts on the main cathodes.

Having described the components of the tube and driving circuit, the action by which the glow is transferred from one main cathode to the next will now be described. Assuming the glow to be taking place at main cathode 12a, a circuit is completed from terminal 16 through resistor 15, to anode 11, to cathode 12a, and through resistor 17 to the terminal 18. Pentode '20 is non-conducting with the consequence that the guide electrodes are at a higher potential than the main cathodes. With the application of a positive input pulse, preferably of square wave form across input terminals 22, the switching action begins. The leading edge of the drive pulse overcomes the bias on the pentode and causes the anode current to increase, which, in turn, by virtue of resistor 15 (which serves as the load resistor for pentode 20) causes a negative going voltage to appear on the anode of the pentode and on the guide electrodes 13, 13a, etc. The circuit parameters are such that the potential on this set of guide electrodes is dropped below that of the main cathodes causing the glow to be transferred, in the present example, to guide electrode 13a. With the reduction of the voltage on the anode of the pentode, the pentode screen current increases, causing a negative going voltage to appear on the screen grid and on guide electrodes 14, 14a, etc. Although the plate current is approximately four times that of the screen, the potential is lowered sufficiently on guide electrodes 14, 14a, etc. to cause guide electrode 14b to be ignited. Thus, while the pulse is on, both guides are ignited, and conduct equally or unequally depending upon the exact parameters of the particular pentode used.

At the termination of the input pulse, the pentode current is cut off causing the voltage on guide electrodes 13, 13a, 1315, etc. to rise thereby extinguishing the glow between guide electrode 13a and anode 11. Although the screen current is also cut off with the termination of the input pulse, the glow discharge remains on guide electrode 14b until the glow current has charged capacitor 21 to a voltage more positive than that of the next adjacent cathode, namely 1212, at which time the glow is extinguished between the anode and guide electrode 14b and transferred onto main cathode 12b. The glow remains at main cathode 12b until the occurrence of another positive going input pulse which causes a repetition of the action described above to transfer the glow from cathode 12b to guide electrodes 13b and Ida, and thence to main cathode 120, with the termination of that pulse. The glow is thus advanced in stepped fashion clockwise of the counter, and upon reaching the main cathode 12a the glow current flowing in resistor 17 produces an output pulse at terminal 19. Thus, in the arrangement illustrated, one output pulse is produced in response to each five input pulses. As was mentioned earlier, however, in a tube having ten main cathodes (3O electrodes in all) and assuming a single output.connection corresponding to that connected to main electrode 12a, one output pulse is derived in response to each ten input pulses.

It will be recognized that should stepping of the glow in the opposite direction be desired, this may be achieved by reversing the connections of the anode and screen grid of the pentode to the guide electrodes.

The described circuit has been found to be reliable at pulse repetition rates of 7000 pulses per second and with a pulse shape which deviates somewhat from rectangular. The capacitor 21 being the only reactive component in the drive circuit, the aperiodicity of the circuit is insured,

' and the characteristics of the pentode insure the overlapping of pulses on the two sets of guide electrodes in response to a single input pulse.

Further modifications of the inventive concepts disclosed herein may now become apparent to those skilled in this art. It will be understood therefore that the scope of the present invention is to be regarded as subject only to those limitations of the appended claims.

What is claimed is:

1. A drive circuit for providing overlapping negative voltage pulses to first and second sets of guide electrodes in a glow transfer tube in response to a positive input pulse comprising, a pentode electron tube having anode, cathode, and control and screen grid electrodes, means directly connecting the anode and screen grid of said pentode to said first and second set of guide electrodes, respectively, a capacitor connected between said screen grid and a point of reference potential, a source of potential more positive than said reference potential connected to the cathode of said pentode, and means for applying said input pulse to the control grid of said pentode.

2. A drive circuit for a glow transfer tube of the type including an anode, a plurality of cathodm, and first and second sets of guide electrodes adapted to provide overlapping voltage pulses to said guide electrodes in re sponse to a positive input pulse comprising, means for applying a voltage between the anode and the cathodes of said counter tube, a pentode having anode, cathode, and control and screen grid electrodes, a connection from the anode of said pentode to said first set of guide electrodes, a connection from the screen grid of said pentode to said second set of guide electrodes, a capacitor connected between the screen grid of said pentode and a point of reference potential, a source of potential more positive than said reference potential connected to the cathode of said pentode and normally biasing said pentode to cut-oft, and means for applying positive input pulses to the control grid of said tube.

3. A drive circuit for a glow transfer counter tube having an anode, a plurality of cathodes and first and second sets of guide electrodes, means for applying a voltage between the anode and cathodes of said counter tube, a pentode having anode, cathode, and screen and control grid electrodes, means respectively connecting the anode and screen grid of said pentode to said first and second set of guide electrodes, at source of potential connected to the cathode of said pentode normally biasing said pentode to cut-off, means for applying a positive input pulse to the control grid of said pentode whereby overlapping negative going potentials are applied to said first and second sets of guide electrodes, and a capacitor connected between said screen grid and a point of reference potential more negative than said source of potential for causing the negative going potential to remain on said second set of guide electrodes for a short period after the termination of said input pulse.

4. Pulse counting apparatus comprising a glow transfer counter tube having an anode, a plurality of main cathodes, and first and second sets of guide electrodes, means connecting the anode of said glow tube to a first source of potential, means connecting said cathodes to a second source of potential of lower value than said first source, a driving circuit for said glow transfer tube including a pentode electron tube having anode, cathode, screen grid and control grid electrodes, means respectively connecting the anode and the screen grid of said pentode to the first and second sets of guide electrodes of said glow transfer counter tube, a capacitor connected between said screen grid and a point of reference potential, a source of potential more positive than said reference potential connected to the cathode of said pentode and normally biasing said pentode to cut-01f, and means for applying input pulses to be counted to the control grid of said pentode.

5. Pulse counting apparatus comprising, in combination, a glow transfer counting tube having an anode, a plurality of main cathodes, and first and second sets of guide electrodes, means connecting the anode of said counter tube to a first source of positive potential, means connecting said main cathodes to a second source of positive potential of lower value than said first source, and a driving circuit for said counter tube comprising a pentode electron tube having at least anode, cathode, control grid and screen grid electrodes, separate means respectively connecting the anode and the screen grid of said electron tube to the first and second sets of guide electrodes of said counter tube, respectively, a capacitor connected between said screen grid and ground, a third source of positive potential of lower value than said second source connected to the cathode of said pentode and normally biasing said electron tube to cut-off, and means for applying positive input pulses to be counted to the control grid of said electron tube, said electron tube when driven into conduction by an input pulse cooperating with said counter tube and said capacitor to provide overlapping ignition pulses to said first and second sets of guide electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,772. Cone Apr. 23, 1946 2,679,978 Kandiah June 1, 1954 2,783,415 Thomas Feb. 26, 1957 

